1. Field of the Invention
The present invention relates to a method of producing a multi-layer ceramic substrate. Specifically, it relates to a method of producing a multi-layer ceramic substrate to be adopted advantageously in the production of a multi-layer ceramic substrate accommodating a passive component such as a capacitor, an inductor, or the like.
2. Description of the Related Art
In order to realize multi-functions, a higher density, and a higher performance in a multi-layer circuit substrate represented by a multi-layer ceramic substrate, it is effective to store a sophisticated passive component and apply wiring with a high density in such a multi-layer circuit substrate.
Multi-layer circuit substrates storing a passive component accordingly have been produced conventionally by various methods as follows:
First one is a so-called thick film method where a dielectric paste, or the like, is printed on substrate green sheets by the thick film forming technology so that the green sheet can be laminated, pressed and baked for partially storing a capacitor, or the like, inside the multi-layer ceramic substrate. However, the method has the following problems:
(1) Due to comparatively large irregularity in the paste film thickness and printing displacement, the irregularity in the capacitor characteristics such as the capacity is comparatively large. PA1 (2) Paste deformation generated in the pressing or baking step gives rise to the irregularity in the characteristics such as the capacity. PA1 (3) Due to deterioration of the flatness in the printing part according to the repetition of printing and lamination, it is difficult to increase the number of the lamination so that a large capacity can hardly be achieved in a capacitor. PA1 (1) Characteristics irregularity due to the printing pattern displacement and the film thickness irregularity, PA1 (2) Capacity limitation due to the difficulty in increasing the number of the lamination, and PA1 (3) Flatness deterioration. PA1 (1) Since a laminated member containing plural kinds of sheets with different compositions is co-sintered, a highly sophisticated technology is required in controlling the contraction behavior and the heat expansion coefficient so as to be coincided in the baking step. PA1 (2) Due to the layer arrangement of the dielectric members inside the substrate, the degree of freedom in design is low. PA1 (3) Problems such as crosstalk of signals can easily be generated. PA1 (1) Due to the layer arrangement of the dielectric members inside the substrate, the degree of freedom in design is low. PA1 (2) Problems such as crosstalk of signals can easily be generated.
Second one is a method similar to the above-mentioned first method, for producing a multi-layer circuit substrate with a resistor and a capacitor where a capacitor, a resistor, or the like is printed on the surface of a ceramic substrate with a thick film forming technology in multi-layers. However, this method has the following problems substantially the same as those of the above-mentioned first method:
Third one is a method of accommodating a dielectric member in a sheet form inside a multi-layer substrate as disclosed in the official gazette of Japanese Unexamined Patent Publication No. 59-17232. In this case, a dielectric sheet having the area the same as the substrate is laminated by being interposed between substrate sheets for the substrate, pressed, and baked. Accordingly, although problems including the characteristics irregularity such as capacity and limitation with respect to a larger capacity can be solved, the following problems come out:
Methods for achieving high density wiring in a multi-layer circuit substrate include a method of pressing onto both upper and lower surfaces of a laminated member comprising a plurality of green sheets for the substrate to be baked at a low temperature, dummy green sheets not to be contracted at the baking temperature of the laminated member for a substrate, baking the same at a comparatively low temperature, peeling off and eliminating the unsintered layer derived from the latter dummy green sheets after baking (see the official gazette of Japanese Unexamined Patent Publication No. 4-243978), and a method of further pressing the laminated member for a substrate from above and below at the time of baking in the above-mentioned method (see the official gazette of Japanese Examined Patent Publication No. 5-503498).
Since contraction can hardly be generated in the substrate surface direction, that is, in the X-Y direction in these methods, the size accuracy of the substrate to be obtained can be improved. Therefore, it is advantageous in that disconnection can hardly be generated even if high density wiring is applied. However, the above-mentioned official gazettes does not disclose the accommodation of a passive component inside the substrate or a technology for facilitating the elimination of the dummy green sheet.
Again, as a fourth method for producing a multi-layer circuit substrate accommodating a passive component, for example, the official gazette of Japanese Unexamined Patent Publication No. 9-92983 discloses a method combining the above-mentioned method of preventing the substrate contraction in the X-Y direction, and the method of partially accommodating a capacitor inside a multi-layer circuit substrate as a sheet or a thick film. This method is suitable for producing a multi-layer circuit substrate accommodating a passive component with high density wiring.
Since a dielectric member layer having the area the same as the substrate is provided when the dielectric member part is formed with a sheet in the fourth method, the dielectric member layer is exposed on the substrate end face. A sufficient density is achieved in the dielectric member layer by pressing the substrate from above and below at the time of baking for the dielectric member layer needs to be dense in order to prevent moisture penetration. However, since the dielectric member layer shape is limited, as in the above-mentioned third method using a dielectric member sheet, problems come out in that:
On the other hand, when the dielectric member part is formed with a thick film in the fourth method, a step of filling a dielectric paste onto a concave part preliminarily provided in the substrate sheet corresponding to the area for forming the dielectric member part can be adopted. Although the problems of the thick film displacement and the characteristics irregularity derived from the dielectric paste deformation can be improved among the problems in the thick film method mentioned above as the first method, the paste film thickness irregularity can be improved but still remains and thus it is still insufficient. Furthermore, due to the difficulty of having the dielectric member part in a laminated structure, a problem of difficulty in obtaining a large capacity still remains.
The fourth method is advantageous in that the contraction in the substrate direction, that is, in the X-Y direction can be considerably smaller so that the contraction irregularity can be smaller accordingly and thus the size accuracy of the substrate can be comparatively high.
However, the fourth method requires the step of peeling off and eliminating the unsintered layer, which cannot contract at the baking temperature of the substrate after baking. If a step of abrasion or homing is needed for the peel-off, it results in the production cost rise therefor. In connection therewith, for example, the official gazette of Japanese Unexamined Patent Publication No. 9-266363 discloses a method of keeping and utilizing the part with a glass component discharged from the substrate surface from the unsintered layer fixed as the substrate surface without peeling off, but in this case, the peeling off step is needed. Moreover, the official gazette of Japanese Unexamined Patent Publication No. 5-136572 discloses a method of utilizing the unsintered layer as the substrate surface by filling the unsintered layer with an organic resin by soaking the same in the organic resin without peeling off or eliminating. In this case, a step of filling with the organic resin is required.